Electrical molding parts such as connector, coil bobbin and housing used in the fields of automotive industry, electrical and electronic industries have heretofore been prepared from polycapramide (nylon 6), polyhexamethylene adipamide (nylon 66) and polybutylene terephthalate (PBT).
However, molded articles obtained from the above-mentioned polycapramide or polyhexamethylene adipamide were not always found to have satisfactory performance when used as electrical molding parts in the fields of automotive industry, electrical and electronic industries. For instance, because of poor water resistance, these molded articles absorb water and undergo dimensional change and change in physical properties. Because deformation (warping) takes place in these molded articles, moreover, there were such problems concerning with resistance to deformation that various troubles such as poor engagement and cracking arise when these molded articles are incorporated into end products. Further, molded articles obtained from the above-mentioned polybutylene terephthalate do not always exhibit sufficient heat resistance, and these molded articles also involved the same problems concerning with resistance to deformation as in the case of the molded articles obtained from the above-mentioned polycapramide or polyhexamethylene adipamide.
Because of excellent mechanical properties and abrasion resistance, polyamides are widely used for sliding parts such as gear, cam and bearing. In this connection, Japanese Patent L-O-P Publn. No. 144351/1985 discloses polyamide resin compositions obtained by melt kneading of 70-98% by weight of polyamide (aliphatic polyamide) and 30-2% by weight of ultra-high-molecular-weight particulate polyethylene having a specific size distribution. However, such aliphatic polyamide resin compositions as disclosed do not always have sufficient heat resistance and self-lubrication, though they are excellent in mechanical properties and abrasion resistance.
Furthermore, Japanese Patent L-O-P Publn. No. 57458/1987 discloses polyamide compositions comprising specific aromatic polyamides and polyamides as those which are excellent in heat-resisting properties, mechanical properties, physicochemical properties and molding characteristics. However, such aromatic polyamide resin compositions as disclosed above have improved heat resistance in comparison with the above-mentioned aliphatic polyamide resin compositions, but the effect of improving heat resistance of said aromatic polyamide resin compositions was not always sufficient and self-lubrication of said compositions was also not always sufficient.
Under these circumstances, the present inventors 0 prosecuted extensive researches with the view of solving such problems associated with the prior art as mentioned above, and have eventually found that injection molded articles which are excellent in balance between toughness and rigidity, impact resistance, heat resistance and water 5 resistance and, at the same time, which are warpless and excellent in resistance to deformation are obtained by carrying out injection molding process using themoplastic resin compositions prepared by mixing in specific proportion, aromatic polyamides comprising specific aromatic dicarboxylic acid component units and specific diamine component units,and high molecular weight modified polyolefins having a specific intrinsic viscosity [.eta.], graft modified with .alpha.,.beta.-unsaturated carboxylic acid, anhydride or derivative thereof and having a crystallinity index of at least 35% or a glass transition temperature of at least 90.degree. C. One the basis of the above finding, the present invention has been accomplished.
In this connection, Japanese Patent L-O-P Publn. No. 144362/1985 discloses polyamide compositions comprising polyamides and modified olefin elastic polymers having a crystallinity index of less than 20%, said composition being alleged to be excellent in mechanical strength such as impact resistance.